[NM020ABG], Technical Note, Thomas Alva Edison, October 8th, 1886


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[NM020ABG], Technical Note, Thomas Alva Edison, October 8th, 1886

Editor's Notes

[drawing] "Patent= Carbonizing under pressure. Z are a number of filiments of organic matter D is a Crucible-- C the cover X a piece of Carbon to prevent the filaments from going upwards; The crucible & cover is made of Carbon ie plumbago D is filled with powdered Lead up to E & from there to the cover with large pieces of Lead The whole is placed in a furnace and gradually brought up to a white heat, when the Lead melts it surrounds the carbons completely and proudces a great pressure on them due to the column of Liquid Lead and as the lead does not boil until the melting point of wrought iron is reached the filaments are perfectly carbonized & consolidated by the pressure; the Lead being liquid allows them to contract without interposing much resistance-- The mould is taken out before the Lead has solidified and poured out leaving a little dross around the carbon which can be removed by acids-- In practice it is preferable to put a small carbon box at the bottom of the crcucible & cover the whole with a powdered alloy of lower melting point than lead so tha the Carbons will be surrounded with a liquid before any great change takes place other metals may be employed such as tin Zinc etc--" 2nd note re 688 689 & 6990 shoujld be separately indexed: "Patent. Filiments are formed from oxides got in a plastic state by mixing a small qunitity of material which combines with the principal oxides such as an alkline silicate in small quanitity mixed with pure oxide of Alumina, Magnesia Zirconia These with water become plastic like clay when finely divided and can be squirted through dies by pressure in the form off cylindrical filiments. These being bent in shape desired are brought upt to a full read heat after wards they are taken out & soaked in a carbonizable compound in a liquid form such as sugar Licorice, etcThis penetrates all the porse and then the whole is put in the furnace in a box with powdered anthracite & brought to a white heat, the walls of the pores & surface are coated with carbonn; as the carbon does not reduce these oxides, the filiment will stand a high temperature-- If it is desired that a lower resistance filiment be obtained a second soaking & recarbonization can be had or the original porcelanic filiment may have incorporated with it a small quantity of the carbonizable compound in this case no alkaline silicate is necessary as the carbon will act as a binder-- The great advantages of filiments made in this manner is that they have very high resistance hence very small copper wire may be used to distribute light over a large area which is of the hightest importance 3rd note: "Patent-- I form a filiment of clay by forcing it through a hole by a press same as they make arc carbons etc-- or roll it out in sheets and stamp the filiment out while plastic if it comes from the die it is bent in shape and slowly baked until nearly all the shrinkage is out-- I then put several in a mould mixed with powdered anthracite coal & bring them up to a white heat-- afterwards they are takin out and put into a tube which can be brought to a white heat a hydrocarbon gas or volatile comound containing carbon is passed through it this deposits carbon over the whole surface of the porcelain filiment, aftewards the porcelain is eaten away by Hydrofluric acid or other solvent. The carbon filimentary shell put in a holder on the ends of the wires running through the inside part of the lamp & electroplated thereto-- any oxides or compound which can be moulded or got in shape while plastic & which will stand a white heat will answer-- plumbago may be rubbed down the surface of the non conducting filiment so that its entire surface becomes a conductor & on passing the current through the fils of plumbago its brot to incandescence & a hard coating is formed on the surface while it is immersed in an atmosphere of a gaseous compound containing carbon-- I an oxide like pure Alumina, Magnesia or Zirconia be used it is infusible hence it will not be necessary to eat it away by acid or other solvent.



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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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